Logical Reasoning

PT151 · S4 · Q24 After a nuclear power plant

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After a nuclear power plant accident, researchers found radioactive isotopes of iodine, tellurium, and cesium but no heavy isotopes-in the atmosphere downwind.

Information

After an accident, they found isotopes of iodine, tellurium, and cesium downwind, but no heavy isotopes.

infer: iodine, tellurium, and cesium are not heavy isotopes

Those three things either came from (1) spent fuel rods or (2) the plant's core.

(1) never has much tellurium in it. (2) would have ejected stuff that included heavy isotopes.

infer: both (1) and (2) have a strike against them, if we assume that this three-pack of isotopes traveled as a bunch. The fact that they had tellurium makes (1) seem like it wasn't the source. The fact that they didn't have heavy isotopes makes (2) seem like it wasn't the source.

After the accident, steam was released from the plant. It may have been in contact with the core, which contains those three isotopes, and those three isotopes are easily dissolved by steam.

Evaluate

What a mouthful! This is a lot to take in, which is why we modeled above some of the self-talk we would be doing while reading it, to try to process where this conversation is headed.

Even though no one is asking any questions, there appears to be a bit of a causal mystery, because researchers found these isotopes, and then we start hearing, "They either came from X or from Y", which makes it seem like we're trying to figure out which one it came from.

We know that the tellurium didn't come from the spent fuel rods, but maybe the other two isotopes did?

We know these three-pack of isotopes didn't eject directly from the core, because if it had then we would have found heavy isotopes in there as well, which we didn't.

There's a possibility that the three-pack of isotopes came from the core, dissolved into steam, which was then released from the plant and then found by researchers downwind from the plant.

But that seems pretty speculative.

Goal

There's so much here that it's hard to make any specific prediction. Let's look for the most supportable answer.

24.

Of the following statements, which one is most strongly supported by the information above?

Radioactive material ejected into the
No Support: no tellurium in core
We know that stuff coming from spent fuel rods wouldn't have tellurium, but we have no idea whether tellurium gets ejected directly from the plant's core. All we know about the plant's core is that heavy isotopes don't get ejected.
7% picked this
Correct
The radioactive material detected by
Why this is right
This seems like plausible story for why the researchers were finding these three isotopes in the atmosphere downwind from the plant. But it's a very speculative story. Steam may have been in contact with the core, in which case it may have picked up the three isotopes from the core, which dissolve easily into steam. (Dissolving kind of means "absorbed into" -- when you dissolve salt into water, the crystals disappear but the salt molecules have not. That's why it now tastes like salt water.) Ultimately, this answer wins because it's more supported than anything else, but it definitely goes down in the record books as one of the more speculative correct answers. Sometimes on Most Supported, the correct answer is pretty distant from the passage, but it's more conservative of a guess than anything else we're offered. Here's another example of a Solve the Causal Mystery style Most Supported question.
Skill tested: Most Supported · how this choice captures the argument's function is the move to repeat next time.
57% picked this
The nuclear power plant's spent
Out of Scope: damage
The passage doesn't talk at all about whether the spent fuel rods were / weren't damaged. We just know that tellurium wouldn't have come from spent fuel rods, regardless of their health / damage.
6% picked this
The researchers found some radioactive
Contradicted
This answer is trying to appeal to students who are thinking that "the iodine and cesium came from the spent fuel rods, but the tellurium was ejected directly from the plant's core". Thus, they would sign off on the idea that some of what the researchers found (the non-tellurium stuff) came from the rods and the rest came from the core. First of all, that's an exotic hypothesis. We're now positing two different sources for where these three isotopes came from, when the passage is offering a different storyline that would only involve on source (steam that passed by the core). Secondly, we can't really sign off on the idea that the researchers found anything that was ejected directly from the core, because we were told that stuff ejected directly would have heavy isotopes, and what researchers found id not have heavy isotopes.
21% picked this
Spent fuel rods do not
No Support
We don't know anything about whether or not spent fuel rods contain heavy isotopes. We only know they don't contain significant amounts of tellurium (which is not a heavy isotopes to begin with).
9% picked this

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